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1、Chapter6:ChemicalBondingSection3:IonicandMetallicBondingPages176-182RBQs#15,17,18,20,21,22,55,59•Aspreviouslyseenanionicbondismadefromametalandanon-metal.◦Metalsformpositiveionscalled_____________________◦Nonmetalsformnegativeionscalled_____________________•Whenpositiveandnegativeionsco
2、mbinesothatthenumberofpositiveandnegativechargesareequal(makingthecompoundneutral)anioniccompoundisformed.◦Forexample,ifacationwitha+1chargeispresent,itneedsananionwitha-1chargetocombinewith◦Orifacationwitha+2chargeispresent,itneedseitherananionwitha-2chargetocombinewith,or2anionseachwi
3、tha-1charge•Recallthatthechemicalformulashowstherelativenumberandtypesofatomspresent•Inioniccompoundsshowsthechemicalformulashowstheratiooftheionspresent•Wherethemolecularformula(chemicalformulaofacovalentcompound)showsthenumberofatomsineachmolecule,thechemicalformulaofanionicsubstances
4、howsthenumberofionsineachformulaunit•Aformulaunitisthesimplestcollectionofatomsfromwhichanioniccompoundformulacanbeestablished.•Inionicbonding,electronsaretransferredfromoneatomtoanothertoformions◦Howdotheelectronaffinitiesofmetalsandnonmetalscompare?◦Howdotheionizationenergiesofmetalsa
5、ndnonmetalscompareExampleofIonicBonding•Whydoatomsformchemicalbonds?•Ionicbondsminimizepotentialenergybycombininginanorderlyarrangementknownasacrystallattice◦Acrystallatticeisathreedimensionalnetworkofpositiveandnegativeionsmutuallyattractedtooneanother•Therepulsiveandattractiveforceske
6、epthedistancebetweentheionsinthecrystalarrangement•Tocomparebondstrengths,latticeenergyisexamined◦Latticeenergyistheenergyneededtoseparateonemoleofanioniccrystallinecompoundintoformedfromgaseousions▪Orlikebondenergy,theamountofenergyneededtobreakthebondsinacrystallattice;again,ameasureo
7、fbondstrength•Ionicbondsandcovalentbondshavecomparablestrengths,dependingontheatomsinvolvedinthebond•PropertiessuchMeltingpoint,boilingpoint,andhardnessdependonhowstrongacompound’sbasicunitsareattracted◦Orinotherwords,howstronglytheatomsinabondareheldtogetherdetermineshowmuchhe
